By: Greg Robidoux | Comments (23) | Related: 1 | 2 | 3 | 4 | 5 | 6 | > Constraints
Problem
Foreign keys (FK) are designed to maintain referential integrity within your database. When used properly FKs allow you to be sure that your data is intact and there are no orphaned records. On the flipside of using FKs to maintain referential integrity, they also become an issue when you need to change table structures or temporarily modify data that might violate the foreign key constraint. Other tips have been written that show you how to identify your FKs and why you should use them, but what is the best approach for manipulating FK constraints to make structure or data changes?
Solution
As mentioned already other tips have been written that show you how to find your foreign keys within your database and why you should use foreign keys. You can refer to these tips for this information:Below is a script that can be used to find all foreign keys that reference the primary table that you wish to work with. In this script you provide the table name and the schema name (object owner). The script will then return a list of statements that can be copied and pasted into a query window to make these changes.
The script also takes three different parameter values depending on the action you want to take:
- DISABLE - this will create the command to disable all FK constraints that reference the table you are working with
- ENABLE - this will create the command to enable all FK constraints that reference the table you are working with
- DROP - this will create a command to drop all FK constraints and create a command to create all FK constraints that reference the table are working with
The values below use a table in the AdventureWorks database, so you can just copy and paste this code and run this sample against that database.
-- Enable, Disable, Drop and Recreate FKs based on Primary Key table
-- Written 2007-11-18
-- Edgewood Solutions / MSSQLTips.com
-- Works for SQL Server 2005
SET NOCOUNT ON
DECLARE @operation VARCHAR(10)
DECLARE @tableName sysname
DECLARE @schemaName sysname
SET @operation = 'DROP' --ENABLE, DISABLE, DROP
SET @tableName = 'SpecialOfferProduct'
SET @schemaName = 'Sales'
DECLARE @cmd NVARCHAR(1000)
DECLARE
@FK_NAME sysname,
@FK_OBJECTID INT,
@FK_DISABLED INT,
@FK_NOT_FOR_REPLICATION INT,
@DELETE_RULE smallint,
@UPDATE_RULE smallint,
@FKTABLE_NAME sysname,
@FKTABLE_OWNER sysname,
@PKTABLE_NAME sysname,
@PKTABLE_OWNER sysname,
@FKCOLUMN_NAME sysname,
@PKCOLUMN_NAME sysname,
@CONSTRAINT_COLID INT
DECLARE cursor_fkeys CURSOR FOR
SELECT Fk.name,
Fk.OBJECT_ID,
Fk.is_disabled,
Fk.is_not_for_replication,
Fk.delete_referential_action,
Fk.update_referential_action,
OBJECT_NAME(Fk.parent_object_id) AS Fk_table_name,
schema_name(Fk.schema_id) AS Fk_table_schema,
TbR.name AS Pk_table_name,
schema_name(TbR.schema_id) Pk_table_schema
FROM sys.foreign_keys Fk LEFT OUTER JOIN
sys.tables TbR ON TbR.OBJECT_ID = Fk.referenced_object_id --inner join
WHERE TbR.name = @tableName
AND schema_name(TbR.schema_id) = @schemaName
OPEN cursor_fkeys
FETCH NEXT FROM cursor_fkeys
INTO @FK_NAME,@FK_OBJECTID,
@FK_DISABLED,
@FK_NOT_FOR_REPLICATION,
@DELETE_RULE,
@UPDATE_RULE,
@FKTABLE_NAME,
@FKTABLE_OWNER,
@PKTABLE_NAME,
@PKTABLE_OWNER
WHILE @@FETCH_STATUS = 0
BEGIN
-- create statement for enabling FK
IF @operation = 'ENABLE'
BEGIN
SET @cmd = 'ALTER TABLE [' + @FKTABLE_OWNER + '].[' + @FKTABLE_NAME
+ '] CHECK CONSTRAINT [' + @FK_NAME + ']'
PRINT @cmd
END
-- create statement for disabling FK
IF @operation = 'DISABLE'
BEGIN
SET @cmd = 'ALTER TABLE [' + @FKTABLE_OWNER + '].[' + @FKTABLE_NAME
+ '] NOCHECK CONSTRAINT [' + @FK_NAME + ']'
PRINT @cmd
END
-- create statement for dropping FK and also for recreating FK
IF @operation = 'DROP'
BEGIN
-- drop statement
SET @cmd = 'ALTER TABLE [' + @FKTABLE_OWNER + '].[' + @FKTABLE_NAME
+ '] DROP CONSTRAINT [' + @FK_NAME + ']'
PRINT @cmd
-- create process
DECLARE @FKCOLUMNS VARCHAR(1000), @PKCOLUMNS VARCHAR(1000), @COUNTER INT
-- create cursor to get FK columns
DECLARE cursor_fkeyCols CURSOR FOR
SELECT COL_NAME(Fk.parent_object_id, Fk_Cl.parent_column_id) AS Fk_col_name,
COL_NAME(Fk.referenced_object_id, Fk_Cl.referenced_column_id) AS Pk_col_name
FROM sys.foreign_keys Fk LEFT OUTER JOIN
sys.tables TbR ON TbR.OBJECT_ID = Fk.referenced_object_id INNER JOIN
sys.foreign_key_columns Fk_Cl ON Fk_Cl.constraint_object_id = Fk.OBJECT_ID
WHERE TbR.name = @tableName
AND schema_name(TbR.schema_id) = @schemaName
AND Fk_Cl.constraint_object_id = @FK_OBJECTID -- added 6/12/2008
ORDER BY Fk_Cl.constraint_column_id
OPEN cursor_fkeyCols
FETCH NEXT FROM cursor_fkeyCols INTO @FKCOLUMN_NAME,@PKCOLUMN_NAME
SET @COUNTER = 1
SET @FKCOLUMNS = ''
SET @PKCOLUMNS = ''
WHILE @@FETCH_STATUS = 0
BEGIN
IF @COUNTER > 1
BEGIN
SET @FKCOLUMNS = @FKCOLUMNS + ','
SET @PKCOLUMNS = @PKCOLUMNS + ','
END
SET @FKCOLUMNS = @FKCOLUMNS + '[' + @FKCOLUMN_NAME + ']'
SET @PKCOLUMNS = @PKCOLUMNS + '[' + @PKCOLUMN_NAME + ']'
SET @COUNTER = @COUNTER + 1
FETCH NEXT FROM cursor_fkeyCols INTO @FKCOLUMN_NAME,@PKCOLUMN_NAME
END
CLOSE cursor_fkeyCols
DEALLOCATE cursor_fkeyCols
-- generate create FK statement
SET @cmd = 'ALTER TABLE [' + @FKTABLE_OWNER + '].[' + @FKTABLE_NAME + '] WITH ' +
CASE @FK_DISABLED
WHEN 0 THEN ' CHECK '
WHEN 1 THEN ' NOCHECK '
END + ' ADD CONSTRAINT [' + @FK_NAME
+ '] FOREIGN KEY (' + @FKCOLUMNS
+ ') REFERENCES [' + @PKTABLE_OWNER + '].[' + @PKTABLE_NAME + '] ('
+ @PKCOLUMNS + ') ON UPDATE ' +
CASE @UPDATE_RULE
WHEN 0 THEN ' NO ACTION '
WHEN 1 THEN ' CASCADE '
WHEN 2 THEN ' SET_NULL '
END + ' ON DELETE ' +
CASE @DELETE_RULE
WHEN 0 THEN ' NO ACTION '
WHEN 1 THEN ' CASCADE '
WHEN 2 THEN ' SET_NULL '
END + '' +
CASE @FK_NOT_FOR_REPLICATION
WHEN 0 THEN ''
WHEN 1 THEN ' NOT FOR REPLICATION '
END
PRINT @cmd
END
FETCH NEXT FROM cursor_fkeys
INTO @FK_NAME,@FK_OBJECTID,
@FK_DISABLED,
@FK_NOT_FOR_REPLICATION,
@DELETE_RULE,
@UPDATE_RULE,
@FKTABLE_NAME,
@FKTABLE_OWNER,
@PKTABLE_NAME,
@PKTABLE_OWNER
END
CLOSE cursor_fkeys
DEALLOCATE cursor_fkeys
Running the script
Here are a few sample outputs that you will get running this against the AdventureWorks database.
Example 1:
- Table: SpecialOfferProduct
- Schema: Sales
- Operation: DROP
ALTER TABLE [Sales].[SalesOrderDetail] DROP CONSTRAINT [FK_SalesOrderDetail_SpecialOfferProduct_SpecialOfferIDProductID] ALTER TABLE [Sales].[SalesOrderDetail] WITH NOCHECK ADD CONSTRAINT [FK_SalesOrderDetail_SpecialOfferProduct_SpecialOfferIDProductID] FOREIGN KEY ([SpecialOfferID],[ProductID]) REFERENCES [Sales].[SpecialOfferProduct] ([SpecialOfferID],[ProductID]) ON UPDATE NO ACTION ON DELETE NO ACTION
Example 2:
- Table: SpecialOfferProduct
- Schema: Sales
- Operation: DISABLE
ALTER TABLE [Sales].[Individual] NOCHECK CONSTRAINT [FK_Individual_Contact_ContactID] ALTER TABLE [Sales].[SalesOrderHeader] NOCHECK CONSTRAINT [FK_SalesOrderHeader_Contact_ContactID] ALTER TABLE [Sales].[StoreContact] NOCHECK CONSTRAINT [FK_StoreContact_Contact_ContactID] ALTER TABLE [Purchasing].[VendorContact] NOCHECK CONSTRAINT [FK_VendorContact_Contact_ContactID] ALTER TABLE [Sales].[ContactCreditCard] NOCHECK CONSTRAINT [FK_ContactCreditCard_Contact_ContactID] ALTER TABLE [HumanResources].[Employee] NOCHECK CONSTRAINT [FK_Employee_Contact_ContactID]
Next Steps
- To make this script more useful and to have this available when needed convert this to a stored procedure.
- Check out more Foreign Key tips
About the author
Greg Robidoux is the President and founder of Edgewood Solutions, a technology services company delivering services and solutions for Microsoft SQL Server. He is also one of the co-founders of MSSQLTips.com. Greg has been working with SQL Server since 1999, has authored numerous database-related articles, and delivered several presentations related to SQL Server. Before SQL Server, he worked on many data platforms such as DB2, Oracle, Sybase, and Informix.This author pledges the content of this article is based on professional experience and not AI generated.
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